The present invention relates to rotary fluid pressure devices, and more particularly, to such devices in which there is a gear-type fluid displacement mechanism and valving to control the flow of fluid to and from the gear set.
Although the invention may be utilized in connection with various types of fluid pressure devices, it is especially adapted for use with low-speed, high-torque gerotor motors and will be described in connection therewith.
Furthermore, although the present invention can be utilized with rotary fluid pressure devices having various types of valving, it is especially suited for use with devices having hollow, generally cylindrical spool valves, wherein the valving action occurs at the interface of the valve spool and the adjacent valve bore defined by the housing.
Low-speed, high-torque gerotor motors have been in commercial use for many years and are especially adapted for applications such as vehicle wheel drives, winch drives and various other vehicle implements. Such motors have been commercially successful partially because the gerotor gear set is uniquely suited to provide the desired low-speed, high-torque output in a compact device which is relatively inexpensive.
In most of the conventional applications for gerotor motors of the type noted above, open-loop control of the flow of fluid to the motor, and of the speed of the motor, have been sufficient. However, there are numerous applications and potential applications for low-speed, high-torque gerotor motors in which more precise flow and speed control are desirable. An example of such an application would be a conveyor drive system in which it is necessary for the conveyor drive motors to operate at, or very close to a predetermined speed.
One approach to providing fairly accurate flow control and speed control for hydraulic motors in applications such as conveyor drive systems has been the use of variable displacement pumps, wherein the displacement of the pump is continuously adjusted to maintain the desired flow through the motor, and therefore, the desired speed of the motor. Although such systems provide generally satisfactory performance, variable displacement pumps are substantially more complicated and expensive than fixed displacement pumps of the same general type, and in systems requiring a substantial number of pumps and motors, it is extremely desirable to be able to provide precise, closed-loop flow and speed control without the need for variable displacement pumps and preferably, without the need for additional system components.